KenandCarolW

I have a '04 600 SB auto 4.10. I pull a 12,000 lb 5vr. When I climb, I routinely engage the Tow/Haul and have alway assumed it accessed the 3rd gear of the 4 speed tranny. The other day I was fooling around and shifted into "2" then back to "D" then engaged the Tow/Haul. The tach was identical (at the same speed of course) when in "2" and when in "D" with Tow/Haul. The natural question that follows would be -- why have Tow/Haul rather than simply shifting into "2"? -- or am I missing something?

cquestad

2 is second....tow haul shuts off overdrive....so you can shift only up to third. Big difference at higher speed...maybe not at 30 mph or so.

BoldtsWagon

I might be wrong on this but, I think the tranny will not downshift to 2nd if you are in OD. It may just downshift into 3rd.

I think you have to be in 3rd, tow/haul on, for the manual shift into 2nd to take effect.

If the tranny shifted from OD directly to 2nd, many undesirable things might happen.

SuperGewl

Kicking into Tow/Haul(O/D OFF) should cause the tranny to kick OFF the OD and drop to 3rd but then it should return to 4th when it can and the OD will remain OFF. This make for AWESOME uphill pulling with load. You can tell as you pass everyone else and they are triing to figure out what you are driving

rmb93243

On my not so AWESOME SO, I click the OD off and it kicks out of 4th. It never returns to 4th, even at the top of the hill, until I push the button again. I like to keep the RPM's around 2300 or so climbing, so when I get down under 1800 I will usually drop it into second (big hills only require this). I'e never tried dropping the lever before pushing the button.

One thing I noticed though, get your foot out of it a bit before you manually upshift 2-3. The TC doesn't lock right away and the RPM's will sail right up to redline!

SuperGewl

Per the Tech Manual, if you have the cruise set & then hit the OD of button this will keep the tranny from shifting from 3rd tho 4th gear which may be thereason you don't see the shift as you stated

OPERATION
At key-on, overdrive operation is allowed. Pressing
the switch once causes the overdrive OFF mode to be
entered and the overdrive OFF switch lamp to be
illuminated. Pressing the switch a second time
causes normal overdrive operation to be restored and
the overdrive lamp to be turned off. The overdrive
OFF mode defaults to ON after the ignition switch is
cycled OFF and ON. The normal position for the con-trol
switch is the ON position. The switch must be in
this position to energize the solenoid and allow a 3-4
upshift. The control switch indicator light illuminates
only when the overdrive switch is turned to the OFF
position, or when illuminated by the transmission
control module.

rmb93243

I'll haveto try that next time I hitch up. Thanks

Truckjerk

You'll most likely find that with any vehicle with an auto. Set cruise in direct drive and it'll hold it until overdrive is re-activated.

KenandCarolW

Hey guys, I think I know how the Tow/Haul works -- I use it quite often. Once again, why is the RPMs the same (at the same speed, of course) in "2" which should be 2nd gear as it is in "D" with Tow/Haul engaged which should be 3rd gear, (shouldn't it??)?